1. Technical Field
The present disclosure relates to a laminated substrate, a light-emitting device, and a method for producing a light-emitting device.
2. Description of the Related Art
In general, display devices, such as liquid crystal displays (LCDs) and organic electroluminescence (EL) displays, have structures in which various layers, such as an electrode layer formed of a metal thin film, a thin film transistor (TFT) layer, an insulating layer, a light-emitting layer, a sealing layer configured to prevent the penetration of water or oxygen from the outside, a color filter, a polarizer, and a protective layer configured to prevent damage due to mechanical stress from the outside, are stacked on a substrate, for example, a glass substrate or a plastic substrate (for example, see Japanese Patent No. 4870156).
The formation of electronic device elements on plastic films (plastic substrates) results in electronic devices characterized by, for example, being lightweight, thin, rugged, and flexible. Such electronic devices are collectively referred to as flexible electronic devices. In recent years, the development of flexible electronic devices has been actively promoted. Examples of electronic devices include displays, photosensors, and radio-frequency identification tags (RFID tags).
Methods for producing such electronic devices including plastic substrates are broadly classified into three methods. A first method includes temporarily fixing a plastic film on a supporting glass substrate, forming an electronic device element, and then separating the supporting substrate. A second method includes forming an electronic device element on a plastic film without using a supporting substrate. A third method includes forming an electronic device element on a supporting substrate and then transferring the electronic device element to a plastic film.
In the second method, the electronic device element is directly formed on the film by, for example, a roll-to-roll process. The dimensions of the film are easily changed because of the absence of a supporting substrate. Thus, the second method has problems with the accuracy of dimensions in pattern processing and the accuracy of registration of patterns. In the third method, when the electronic device element formed on the supporting glass substrate is transferred to the plastic film, the plastic substrate that supports the electronic device element is temporarily not present under the electronic device element. Thus, the electronic device element is likely to break at the time of transfer because of its low mechanical strength. This occurs markedly at a wiring portion that should be arranged outside the plastic film in order to establish electrical connection. In the first method, a conventional apparatus for producing an electronic device can be used, thus suppressing investment in equipment. Moreover, the electronic device element is fixed on the supporting glass substrate in the production process, thus resulting in excellent dimensional stability during processing. After the separation of the supporting substrate composed of glass, the mechanical strength is maintained because of the presence of the plastic film. The first method has the advantage that the device can be easily produced.
In the case where an electronic device is produced by the first method, it is necessary to separate a supporting glass substrate after the formation of an electronic device element. In this case, however, a high-temperature heating step and so forth are performed in the process of forming the electronic device element after the temporary fixation of the plastic film on the supporting glass substrate. The plastic film and the supporting glass substrate are less likely to be easily separated from each other because of high adhesion between the plastic film and the supporting glass substrate.
To address this problem, Japanese Patent No. 4870156 discloses a method for separating a supporting glass substrate by cutting a contact portion of an interface between the supporting glass substrate and a plastic film with a laser.
To more stably performing the separation in the method for separating a supporting glass substrate with a laser disclosed in Japanese Patent No. 4870156, Japanese Patent No. 3809681 discloses a separation-promoting method in which an amorphous silicon layer is provided between a supporting glass substrate and a plastic substrate, and laser irradiation is performed to generate hydrogen gas from the amorphous silicon layer.